Merge pull request #400 from ndawe/master

[MRG] histfactory.utils kwargs bug
make middle hist optional in get_band
Merge pull request #402 from ndawe/master

[MRG] make middle hist optional in get_band
Merge pull request #401 from ndawe/roosh

[MRG] roosh: better canvas/style handling
consistently index axis from 0 to 2
Merge pull request #403 from ndawe/axis

[WIP] consistently index axis from 0 to 2
fix broken underflow() and overflow() methods
Merge pull request #404 from ndawe/axis

[MRG] fix broken underflow() and overflow() methods
hist: add set_sum_w2 and get_sum_w2 methods
hist: implement merge_bins method to merge arbitrary sets of bin windows
unit tests for merge_bins, overflow, and underflow
add bin merging example
Merge pull request #405 from ndawe/master

epic bin merging algorithm
add missing SetPalette(1) to ATLAS and CMSTDR styles
plot_hist_fill_array: increase right margin in 2d/3d plotting examples and remove colour bar
Merge pull request #406 from ndawe/style

[MRG] style: missing SetPalette(1) in ATLAS and CMSTDR
examples: speedup for plot_bin_merging.py in batch mode
examples: tree_to_array.py speedup (use fewer entries)
examples: speedup chain_overwrite.py by using fewer files and entries in each
examples: speedup plot_autobinning.py in batch mode